December 1945 Charles H. Kaman left the company of Igor Sikorsky and at the age of 26 formed Kaman Aircraft Company with the goal to develop and produce helicopters with contra-rotating intermeshing rotors that eliminates the need of a tail rotor. The first helicopter was the two-seat K-125A (NX63077) powered by an 125 hp Lycoming engine, the maiden flight taking place on January 15, 1947. This was developed into the 190 hp Lycoming-powered K-190A (NX74105) flown in 1948.

The K-190A served as the prototype for a 225 hp Lycoming O-435-2 piston engine production derivate, the two-seat K-225 flown also in 1948. Both the K-190A and the K-225 gained the CAA type certificate in April 1949 and these early machines were leased by Kaman for civil duties, including crop dusting. The first military orders came in 1950 from the Bureau of Aeronautics of the US Navy for two K-225s, no military designation was assigned although they did have bureau numbers 125476 and 125477, while the USCG ordered one, s/n 1239. The K-225 was the first gas turbine powered helicopter in the world ion on December 10, 1951.

Evaluation of the K-225 by the Navy led to an order for 29 K-240s with the designation HTK-1. Primary a trainer it provided seating for a pilot, a co-pilot/student and a passenger, or in the ambulance role a stretcher; even ASW duties have been performed. The USAF evaluated one Navy HTK-1 under the designation YH-22, s/n 50-1271. Another, BuNo. 129344, was adapted to the HTK-1K remotely-controlled drone under a joint Navy-Army program. Flown for the first time on July 30, 1957, it was intended to be used in dangerous missions like delivering explosives, rescuing personnel, reconnaissance, etc. The HTK-1 had also a first when BuNo. 128657 was fitted with two Boeing YT50 turboshafts; it became the worlds first twin gas turbine powered helicopter flying so on March 26, 1954. All remaining HTK-1s were redesignated to TH-43E in 1962.